1. Field of the Invention
The present invention relates to wind turbines. More particularly, the invention relates to an auxiliary drive/brake system for use in conjunction with a wind turbine.
2. Description of the Related Art
A wind turbine is not generally a reliable method for electricity generation because it depends entirely on the presence and strength of the wind in order to operate. Wind turbines cannot generate electricity when the wind speed is too low, the wind is intermittent, the wind speed drops rapidly and suddenly, or the wind speed is too high. The variable and random nature of the wind makes it difficult for power companies to use wind turbines for reliable electricity generation because changes to the wind create an immediate change in the amount of electricity available for transmission.
The greatest problem is when the wind speed drops rapidly and suddenly and forces multiple wind turbines to stop producing electricity. The resulting rapid and immediate drop in electricity output causes a large shortage of electricity that power companies must replace quickly in order to avoid creating a blackout or a brownout of its customers as well as overload damage of its electricity transmission system.
As shown with reference to Graph #1 shown in FIG. 10, a conventional 1.5 MW wind turbine for this example is capable of producing its nameplate (100% full load rating) of electricity only when the wind speed is sufficient to keep the wind turbine rotor blades 7 operating above 10 rpm. The minimum wind speed value required for 100% full load rating in 25 mph.
When the wind speed drops below 25 mph it causes the wind turbine rotor blades 7 speed (rpm) to fall below 10 rpm. This speed reduction causes the quantity of electricity the wind turbine 200 can generate to decrease rapidly because the power curve enters into the ramp up/ramp down period of operation (4 to 10 rpm).
The power curve for the ramp up/ramp down period of operation has a steep slope and demonstrates that when the wind speed falls by 50% from the full load value (25 mph/2=12.5 mph) the wind turbine can lose 80% of its generation ability (12.5 mph correlates to 0.27 MW
As those skilled in the art will certainly appreciate, and with reference to FIG. 1 the basic wind turbine is composed of wind turbine rotor blades 7 connected to the wind turbine low-speed shaft 8. The wind turbine low-speed shaft 8 drives the wind turbine gearbox 9 by means of the input shaft 10 of the wind turbine gearbox 9. The output shaft 11 of the wind turbine gearbox 9 drives the wind turbine high-speed shaft 12. The wind turbine high-speed shaft 12 connects to the input shaft 13 of the wind turbine generator 14. The wind turbine generator 14 produces the electricity that is supplied to the electricity transmission network of the power company. The wind turbine rotor blades 7 are powered by wind only. This restricts the wind turbine generator 14 because the wind turbine generator 14 can only produce electricity when wind is available to turn the wind turbine rotor blades 7 at the required rpm (shaft speed).
The yaw control mechanism rotor blades 31 are used to position the wind turbine rotor blades 7 to further engage or disengage the wind, and the input shaft brake mechanism 33, provided the wind turbine is equipped with it, is used to slow the wind turbine low-speed shaft 8 and the wind turbine rotor blades 7 if these rotate above the maximum allowable rpm (shaft speed). The wind turbine gearbox 9 and the wind turbine generator 14 are installed on the base plate 20. The base plate 20 is attached to the wind turbine tower 22 by the rotating joint 21. The rotating joint 21 allows the wind turbine to rotate in the horizontal plane (yaw) about the wind turbine tower 22 whenever the wind changes direction. The wind turbine nacelle 37 covers and protects the internal components of the wind turbine.
As discussed above, current wind turbines are not generally reliable for use in electricity generation because they depend entirely on the presence and strength of the wind in order to operate. As result, a need exists for a mechanism by which wind turbines may be used in a variety of wind conditions so as to make them commercially feasible for implementation by power companies.